September 1, 2014

The sea level around the coast of Antarctica is expected to rise faster than the projected global rate, experts from the University of Southampton report in research appearing Sunday in the advanced online edition of the journal Nature Geoscience.

In the paper, lead author Craig Rye and colleagues from the National Oceanography Centre, the British Antarctic Survey and the Scottish Association for Marine Science explain that satellite data from the past 19 years revealed that melting glaciers have caused the sea level there to rise by 2 cm more than the global average of 6 cm.

The researchers said they detected this rapid increase in sea level after studying satellite scans of an area spanning more than one million square kilometers. They added that melting of the Antarctic ice sheet and thinning of floating ice shelves has added an estimated 350 gigatons of additional freshwater to the surrounding ocean.

As a result, the salinity of the ocean water has reduced (a fact that the study authors said has been corroborated by ship-based studies of the water), and Rye explained that since freshwater is less dense than salt water, regions that have accumulated an excess of the former are expected to experiences a localized increase in sea level.

The authors said that most of this increase in freshwater has been found in the region around the Antarctic Peninsula and the Amundsen Sea, and by using the satellite measurements in combination with computer simulations of ocean circulation, they found that the region was experiencing sea level increases greater than the regional mean.

“On the basis of the model simulations, we conclude that this sea-level rise is almost entirely related to steric adjustment, rather than changes in local ocean mass, with a halosteric rise in the upper ocean and thermosteric contributions at depth,” they wrote. “We conclude that accelerating discharge from the Antarctic Ice Sheet has had a pronounced and widespread impact on the adjacent subpolar seas over the past two decades.”

In other words, the sea rise increasing in the Antarctic is due primarily to halosteric (due to the influx of freshwater), while deeper waters are being affected by increases in water temperature, or thermosteric changes. The results of the computer simulation matched closely with the real-world data obtained by the satellites, the authors said.

“The computer model supports our theory that the sea-level rise we see in our satellite data is almost entirely caused by freshening (a reduction in the salinity of the water) from the melting of the ice sheet and its fringing ice shelves,” said Rye, who oversaw the data analysis and was the corresponding author on the study.

“The interaction between air, sea and ice in these seas is central to the stability of the Antarctic Ice Sheet and global sea levels, as well as other environmental processes, such as the generation of Antarctic bottom water, which cools and ventilates much of the global ocean abyss,” he added.

Last month, researchers from the Alfred Wegener Institute (AWI) in Germany used data the European Space Agency’s (ESA) CryoSat-2 spacecraft has been used to accurately map elevation changes in Antarctica, and found that the ice sheet there was reducing in volume by approximately 125 cubic kilometers per year.